A cook frequently needs to periodically add a small quantity of liquid to a cookpot while same is on the heat. To save the cook the repeated chore of opening up the pot and pouring in the necessary small quantity of liquid, it has been suggested to provide a cookpot lid with a reservoir and structure allowing the liquid to drip down into the pot at a controlled and relatively slow rate.
Such a pot typically has a piece of porous material forming the floor of a cup-shaped reservoir. The material to be dosed into the pot therefore seeps through this porous floor.
The disadvantage of this construction is that the porous material through which the liquid seeps can clog. Furthermore the dosing rate cannot be varied, so that if the dosing rate is too fast the user must add the liquid manually, and if it is too slow extra must be added periodically by hand. Finally the porous material is normally very difficult if not impossible to clean.